On the Nerve Supply of the Nasopalatine Duct and the JACOBSON's organ of Dog in the Later Fetal Stage

Abstract

In the hard palate of a fetus of dog in the later stage, the development of the sensory fibres and especially of their terminations is very poor, as poor as the papillary formation out of the propria into the epithelium is in this part, a small number of unbranched and very simple branched terminations being barely found beneath the epithelium. Intraepithelial fibres too are present in an extremely small number, consisting in very thin fibres ending without branching.The respiratory part of the nasal cavity of dog's fetus is covered by a 5-rowed ciliated epithelium containing frequent goblet cells and nasal glands and venous plexus are formed in the subepithelial loose connective tissue. In this respiratory part are found many vegetative fibres in distribution but sensory fibres here are very scanty and their terminations are not yet definitely completed, no intraepithelial fibres being yet observable.The nasopalatine duct and the so-called JACOBSON's orgen or canal are, however, both in very conspicuous formation already. The nasopalatine duct opens out in front of the hard palate at the ventralmost end. Its histology is considerably different from that of the duct of cattle fetus (SUGIMOTO). In dog's fetus, the distal one-third of the nasopalatine duct is lined with a stratified flat epithelium thinner than that of the hard palate and interspersed with islets of cylindrical epithelium. The middle one-third of the duct has a wide lumen lined with a stratified cylindrical epithelium. In the more dorsal part, the duct narrows down, the epithelium regains the stratified flat type and running steeply up dorsocranially, the duct opens out into the nasal cavity. Such mucous glands as found around the nasopalatine duct in cattle fetus are never found in canine fetus.The nasopalatine duct of cattle fetus is very rich in sensory fibres and their subepithelial and intraepithelial terminations, but the duct of my canine fetus was found so incomparably poor in sensory nerve supply, for the number of the small nerve bundles in the subepithelial tissue was very small and the sensory fibres in such a bundle were again very few. These fibres are always of medium size and their terminations are usually nothing but unbranched or very simple branched terminations, of which the terminal fibres, without showing perceptible change in size or winding in their courses, end sharply just beneath the epithelium. But rather more complex branched terminations are not entirely absent. Intraepithelial fibres, usually of unbranched type, were fonnd in an extremely small number, as in the hard palate.The JACOBSON's organ of dog's embryo ends in a blind sac dorsalwards, but ventralwards it opens out into the distalmost part of the nasopalatine duct. This foremost part is lined with a 2-3-rowed cylindrical epithelium and the posterior blind sac with a 1-2-rowed cylindrical epithelium. The largest part of this canal except these two ends is lined with the so-called olfactory nouroepithelium on its medial wall and with a thinner 2-rowed cylindrical epithelium on its lateral wall. The connective tissue layer around this canal is rich in blood vessels, but in my specimen, no such glands as found in the counterpart of some other fetal mammals could be ever detected.On the medial side and the lateral side of the JACOBSON's organ some nerve branches of nn. olfactorii and a very few fine nerve bundles from the n. trigeminus were found running in, respectively. The trigeminal sensory fibres were found extremely small in number, as in the nasopalatine duct, and their terminations were merely of unbranched and simple branched types sparsely formed subepithelially and intraepithelially.The relation between the so-called smell neuroepithelium and the olfactory fibres on the medial side of the JACOBSON's canal of my dog's fetus was incompatible with that postulated by SCHULTZE and concordant with the finding of SAITO on human fetus.